Backups of data and keeping thereof are essential to deal with data missing due to a disaster and the like. In an actual disaster, the backup data will be utilized to perform restoration. In recent years, however, since an amount of data to be handled, as referred to as “big data,” has tended to increase and also led to a huge amount of backup data, the time required for the restoration has tended to be prolonged. As a backup technology for the purpose of quick recovery of such a file system, for example, JP2013-254513A, has been known.
In addition, tape media are often used as inexpensive backup media. Commonly, in operation, the backup data is saved on tapes while the data is retained on a disk. In a disaster, a method is employed in which all the backup data is read out from the tapes and recovered in a state accessible from the disk. In such a scheme, however, since work cannot be resumed until the data is read out from all the tapes, the recovery takes a very long time.